Controllable preparation of mesoporous silica and its application in enzyme-catalyzed CO₂ reduction

Enzymatic conversion of CO₂ to high-value chemicals is a significant route for the utilization of greenhouse gases in mild, high-selectivity and environment-friendly way, however, conversion efficiency is not yet satisfying. Here, mesoporous silica (mSiO₂) nanoparticles with controllable structure were prepared and modified by polydopamine (PDA) and polyethyleneimine (PEI), which were then used in an integrated process for CO₂ capture and conversion to formate for the first time. The effects of structure parameters of mSiO₂ and modification conditions on its application properties were investigated. The results show that in a range of 230 ∼ 500 nm, SiO₂ particles with smaller size exhibited better intensifying effect, while the optimal size was 410 nm for mSiO₂ with the same etching extent, attributed to a higher specific surface area. mSiO₂ itself was a robust CO₂ adsorbent and the addition of 0.01 g mSiO₂₍₄₁₀₎ enabled CO₂ conversion to be accelerated 11.94 times compared to free enzyme. After modification, with 0.05 g PDA/PEI-mSiO₂₍₃₄₀₎ and PDA/PEI-mSiO₂₍₄₁₀₎, the enzyme reaction was expedited up to 24 and 30.8 times of the system without particles due to an enhanced CO₂ uptake, as a collaborative result of mesoporous structure and amino-functionalization. Following that, PDA/PEI-mSiO₂₍₄₁₀₎ was used as the carrier for the co-immobilization of formate dehydrogenase and carbonic anhydrase, which could retain 86.7% activity after use for 10 times and 55.2% activity after 21 days at 4 °C, while 29.6% for free enzymes.